A typical inflator assembly includes a rupturable burst disk which, when ruptured, releases a flow of gas from a container in which gas is stored to an air bag to inflate the air bag. The burst disk is ruptured in response to a vehicle collision. In known inflator assemblies which include a rupturable burst disk, the opening created by the ruptured burst disk is a factor in determining the rate of gas flow into the air bag. It is important, therefore, to have the burst disk reliably rupture to create an opening with an effective flow area in a predetermined range of areas.
A known inflator assembly for inflating an inflatable vehicle occupant restraint, such as an air bag, is disclosed in U.S. Pat. No. 5,131,680. An inflator assembly disclosed in the '680 patent includes a container which stores gas under pressure for inflating the vehicle occupant restraint. The inflator assembly further includes a body of pyrotechnic material disposed within the container. The inflator assembly also includes an actuatable igniter assembly for, when actuated, igniting the body of pyrotechnic material. The igniter assembly includes an ignition material which rapidly burns at a relatively high temperature to generate heat and flame which in turn initiates burning the body of pyrotechnic material. As the body of pyrotechnic material burns, flame and hot combustion products emitted by the body of pyrotechnic material pressurize and supplement the stored gas.
The inflator assembly disclosed in the '680 patent also includes an actuator assembly which operates in response to vehicle deceleration indicative of a collision. The actuator assembly is operable to actuate the igniter assembly and to rupture a burst disk to release a flow of gas from the container. The actuator assembly includes an ignition material which, when ignited, generates pressure against the head of a piston to move the piston. The moving piston ruptures the burst disk and strikes the igniter assembly to ignite the ignition material of the igniter assembly. The ignition material, in turn, ignites the body of pyrotechnic material within the container.
Another known inflator assembly for inflating an inflatable vehicle occupant restraint, such as an air bag, is disclosed in co-pending U.S. patent application Ser. No. 965,356, filed on Oct. 23, 1992, entitled "Air Bag Inflator," and assigned to the assignee of the present application. An inflator disclosed in the co-pending application includes a source of gas for inflating the occupant restraint. A burst disk is located to block gas flow into the occupant restraint. A piston is provided for rupturing the burst disk. The piston is movable from a retracted position to an extended position to rupture the burst disk. The piston includes (i) a first central portion for puncturing the burst disk and (ii) a second portion for cutting out a portion of the burst disk after the first central portion punctures the burst disk. The cut portion of the burst disk is clamped between the piston and a housing part of the inflator.
Another known inflator assembly for inflating an inflatable vehicle occupant restraint, such as an air bag, is disclosed in co-pending U.S. patent application Ser. No. 947,147, filed on Sep. 18, 1992, entitled "Apparatus for Inflating a Vehicle Occupant Restraint", and assigned to the assignee of the present application. An inflator disclosed in the co-pending application includes a container which holds a combustible mixture of gases which is ignited. The container has an end wall which bursts when a predetermined pressure is reached in the chamber. When the end wall bursts, gas flows into the occupant restraint.